1. Field of the Invention
The present disclosure relates to a wire mesh type diffuser plate and a liquid crystal display device having the same, and particularly, to a wire mesh type diffuser plate used in a direct type backlight unit, a method of fabricating the same, and a liquid crystal display device having the same.
2. Related art of the Invention
A liquid crystal display (LCD) device is a display device in which data signals according to image information are individually supplied to pixels arranged in a matrix form and light transmittance of the pixels is adjusted to display a desired image.
Thus, the LCD device includes a liquid crystal panel in which pixels are arranged in a matrix form and a driving unit for driving the pixels.
The liquid crystal panel includes a color filter substrate and an array substrate attached in a facing manner with a uniform cell gap maintained therebetween, and a liquid crystal layer formed in the cell gap between the color filter substrate and the array substrate.
Here, a common electrode and a pixel electrode are formed on the liquid crystal panel formed by attaching the color filter substrate and the array substrate to apply an electric field to the liquid crystal layer.
Thus, in a state in which a voltage is applied to the common electrode, when a voltage of a data signal applied to the pixel electrode is controlled, liquid crystal of the liquid crystal layer rotates by dielectric anisotropy according to an electric field between the common electrode and the pixel electrode, thereby displaying characters or images by transmitting or blocking light by pixels.
Here, the LCD device is a light receiving device that does not emit light by itself. That is, because the LCD device displays an image by adjusting transmittance of light coming from the outside, it requires a backlight unit.
A related art LCD device will be described in detail with reference to the accompanying drawings.
FIG. 1 illustrates a sectional view schematically showing a portion of a structure of a related art LCD device.
As illustrated, a related art LCD device includes a liquid crystal panel 10 on which pixels are arranged in a matrix form to output an image, a driving unit (not shown) for driving the pixels, a backlight unit installed on a rear surface of the liquid crystal panel 10 to emit light to a front surface of the liquid crystal panel 10, and a panel guide 25 receiving the liquid crystal panel 10 and the backlight unit and fixing them.
Here, the liquid crystal panel 10 includes a color filter substrate 1 and an array substrate 11 attached in a facing manner with a uniform cell gap maintained therebetween, and a liquid crystal layer formed in the cell gap between the color filter substrate 1 and the array substrate 11.
Although not illustrated, a common electrode and a pixel electrode are formed on the liquid crystal panel 10 formed by attaching the color filter substrate 1 and the array substrate 11 to apply an electric field to the liquid crystal layer. In a state in which a voltage is applied to the common electrode, when a voltage of a data signal applied to the pixel electrode is controlled, liquid crystal of the liquid crystal layer rotates by dielectric anisotropy according to an electric field between the common electrode and the pixel electrode, thereby displaying characters or images by transmitting or blocking light by pixels.
In order to control a voltage of a data signal applied to the pixel electrode by pixels, a switching element such as a thin film transistor (TFT) is individually provided in the pixels.
Upper and lower polarization plates (not shown) are attached to an outer side of the liquid crystal panel. The lower polarization plate polarizes light passing through the backlight unit, and the upper polarization plate polarizes light passing through the liquid crystal panel 10.
The backlight unit used as a light source of the liquid crystal panel is classified into an edge type backlight unit and a direct type backlight unit according to a method of disposing a light emitting lamp.
In the direct type backlight unit, a light emitting lamp 21 is disposed below the liquid crystal panel 10 to supply light. In detail, in the direct type backlight unit, a plurality of lamps 21 are disposed as light sources, and a reflector 22 is positioned under the plurality of lamps 21. A plurality of optical sheets 24 are laminated and positioned above the plurality of lamps 21.
Here, because the direct type backlight unit does not use a light guide plate, a diffuser plate 23 is provided between the plurality of lamps 21 and the optical sheets 24 in order to diffuse light of the lamps and support the optical sheets 24.
Also, although not illustrated, a conical fixing support is provided in order to support the diffuser plate 23 and the optical sheets 24 provided in the upper portion of the lamps 21.
The liquid crystal panel 10 including the color filter substrate 1 and the array substrate 11 is mounted through the panel guide 25 in an upper portion of the backlight unit configured as described above. The liquid crystal panel 10, the panel guide 25, and the backlight unit are coupled by a lower cover bottom 30 and an upper case top 35 through a plurality of fastening units 40a and 40b to form an LCD device.
As a material of the diffuser plate 23, polymethacryl styrene (MS), polystyrene (PS), polycarbonate (PC), or the like, is mainly used, and tolerance to thermal deformation and moisture and UV stability are required.
FIG. 2 illustrates a sectional view showing a structure of a related art diffuser plate shown in FIG. 1, for example.
As shown in the drawing, for example, an existing diffuser plate 23 has a tri-layer structure in which plastic called polymetacryl styrene 23b is provided on both sides of polystyrene 23a provided in the middle portion.
The diffuser plate 23 is fabricated through an extruding method. A polymer chip as a raw material is put in an extruder, discharged through a T-die, and then, passes through a roll so as to be fabricated.
The diffuser plate 23 has a thickness of 1.2 mm, 1.5 mm, 2.0 mm, or the like, and the thickness of the diffuser plate 23 is increased as an application inch of a liquid crystal panel is increased in order to secure reliability.
The fabricated diffuser plate 23 is deformed due to moisture absorption, generating egg mura in the liquid crystal panel.
FIGS. 3A and 3B illustrates sectional views showing a mechanism of generating egg mura.
With reference to these drawings, in the case of the direct type backlight unit, because the lamp 21 as a light source exists below the diffuser plate 23, the lower side has a high temperature and the liquid crystal panel 10 side has a low temperature, so a temperature difference between the spaces generate moisture M.
Here, the diffuser plate 23 absorbs the moisture M so as to be expanded toward the liquid crystal panel 10, and the expansion of the diffuser plate 23 lifts the surface of edges of the liquid crystal panel 10 to generate egg mura having an egg shape. Moisture M in a surrounding environment also makes the same influence.
That is, because the polarization plate, the optical sheets 24, and the diffuser plate 23 absorb moisture M in a high temperature and high moisture environment, when the backlight unit is driven, the liquid crystal panel 10, the optical sheets 24, and the diffuser plate 23 are warped. Here, a contact portion and a non-contact portion exist between the lower polarizer plate and the optical sheets 24, and due to a different in moisture evaporation between the contact portion and the non-contact portion, the spots in the form of an egg mura are formed in the liquid crystal panel 10.
In order to improve this, the diffuser plate 23 is required to have a predetermined thickness, which makes it difficult to implement a slim design.
Also, when the thickness of the diffuser plate 23 is reduced, a resin flows down, non-molding, or the like, are generated in terms of the characteristics of the existing extruding process, having a limitation in reducing the thickness of the diffuser plate 23. That is, the thickness of the diffuser plate 23 is determined by passing a polishing roller during extruding, and in order to prevent a generation of non-molding, a predetermined thickness of the diffuser plate 23 should be maintained.